feat: accept taxonomy_type on taxonomy create and import endpoints

[alezconsultant]

Description

Adds taxonomy_type to the taxonomy create and import endpoints: "competency"
creates a CompetencyTaxonomy alongside the base Taxonomy, "tags" (default)
creates a plain one.

This PR lands the openedx-core side only. A companion PR against
openedx-platform will wire TaxonomyOrgView to CompetencyTaxonomyView and
pass taxonomy_type through from the client.

Changes

• src/openedx_tagging/api.py: TaxonomyType enum (TAGS, COMPETENCY).
• src/openedx_tagging/rest_api/v1/serializers.py: taxonomy_type, a write-only
  ChoiceField on TaxonomySerializer, default "tags".
• src/openedx_tagging/rest_api/v1/views.py: TaxonomyView.perform_create() and
  create_import() discard taxonomy_type after validation — this app must never
  import openedx_learning. create_import()'s taxonomy-creation step is extracted
  into an overridable _create_taxonomy_for_import() hook.
• src/openedx_learning/applets/cbe/api.py: create_competency_taxonomy() — creates
  the Taxonomy and linked CompetencyTaxonomy rows in one transaction.
• src/openedx_learning/applets/cbe/views.py (new): CompetencyTaxonomyView, a
  TaxonomyView subclass overriding perform_create()/_create_taxonomy_for_import()
  to dispatch to create_competency_taxonomy() for taxonomy_type="competency".

Design notes

• openedx_tagging stays unaware CompetencyTaxonomy exists (lint-imports enforces
  it never imports openedx_learning). Plain TaxonomyView accepts
  taxonomy_type="competency" as a valid value but always creates a plain Taxonomy
  for it, since it structurally can't do anything else.
• CompetencyTaxonomyView overrides TaxonomyView's creation methods rather than
  building on top of them, because that layering rule blocks the other direction:
  openedx_tagging can't extend itself with competency-aware behavior, since it
  can't reference openedx_learning at all. Overriding in a subclass that lives in
  openedx_learning (where both apps are visible).
• CompetencyTaxonomyView is a real subclass, not a mixin: one consumer for now
  (openedx-platform's TaxonomyOrgView).

Verification

• pytest tests/openedx_learning tests/openedx_tagging --no-cov: 492 passed.
• pylint, pycodestyle, isort --check-only, mypy, lint-imports: all clean.

Related to #628

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[mgwozdz-unicon]

Claude and I worked together on this code review and are requesting the enumerated changes below. The layering is done right: openedx_tagging's serializer and view changes never import or reference openedx_learning/CompetencyTaxonomy anywhere, create_competency_taxonomy() is the only place that touches both packages, and lint-imports confirms both contracts still hold. That matches the architecture constraint in #614 ("openedx_tagging must not import or instantiate CompetencyTaxonomy").

1. CompetencyTaxonomyView.perform_create() returns a 500 instead of a 400 on a validation failure.

In src/openedx_learning/applets/cbe/views.py, the competency branch of perform_create() calls create_competency_taxonomy(**serializer.validated_data) directly, with no error handling. The base TaxonomyView.perform_create() (the branch taken for "tags", in src/openedx_tagging/rest_api/v1/views.py) wraps the equivalent call in try/except exceptions.ValidationError and re-raises DRF's ValidationError so it comes back as a 400. The competency branch skips that.

Claude reproduced it: create_competency_taxonomy() calls create_taxonomy() internally, which calls taxonomy.full_clean(). Posting taxonomy_type="competency" with an export_id that already exists raises django.core.exceptions.ValidationError from that full_clean() call, and it propagates unhandled, so the response is a 500. The same duplicate export_id through plain TaxonomyView returns a 400. Can you wrap the competency branch's call the same way the base class does, so both paths return a 400 on the same kind of failure?

2. Please add a test that exercises CompetencyTaxonomyView itself.

Every new test in tests/openedx_tagging/test_views.py posts to TAXONOMY_LIST_URL / TAXONOMY_CREATE_IMPORT_URL, which route to plain TaxonomyView (see src/openedx_tagging/rest_api/v1/urls.py), not CompetencyTaxonomyView. The two new methods on CompetencyTaxonomyView, i.e. the actual taxonomy_type dispatch this ticket exists to add, have no test going through the view at all. That's how item 1 got through. CompetencyTaxonomyView isn't registered on a URL in openedx-core yet, but it can still be tested directly via APIRequestFactory + .as_view() without one. At minimum: the competency branch of perform_create() returns a CompetencyTaxonomy, and it returns a 400 (not a 500) on a validation failure, same as the "tags" branch.

3. test_create_taxonomy_type_tags_or_omitted and test_import_taxonomy_type_tags_or_omitted claim more than they check, and nothing else in the repo checks it either.

Both docstrings say the endpoint "creates a plain Taxonomy" with no way to create a CompetencyTaxonomy row, but both only assert Taxonomy.objects.filter(name=...).exists(). Since CompetencyTaxonomy is multi-table inheritance from Taxonomy, that assertion would pass either way, so it doesn't test the claim. It looks like there's no test_views.py under tests/openedx_learning/ at all, so nothing in the repo actually asserts that a CompetencyTaxonomy row is absent here. Since tests/openedx_tagging can't import CompetencyTaxonomy without breaking the layering rule it's demonstrating, can you add that assertion as its own test in tests/openedx_learning, with a docstring describing what it actually checks, and amend these two docstrings to only claim what their own assertions verify?

4. The comment on where export_id gets auto-generated got dropped, and the replacement docstring doesn't cover it.

The old create_import() had # If no taxonomy_export_id provided, a unique export id will be generated above the create_taxonomy() call. That's gone, and the new _create_taxonomy_for_import() base method doesn't explain it either. create_taxonomy()'s own docstring in src/openedx_tagging/api.py still just says "Creates, saves, and returns a new Taxonomy with the given attributes," it never documents the auto-generation behavior (if not export_id: export_id = f"{count+1}-{slug}").

Rather than restoring that exact comment at one call site, can you add a line to create_taxonomy()'s own docstring instead? After this PR there are three places that can pass export_id=None into that auto-generation path: the base _create_taxonomy_for_import(), CompetencyTaxonomyView._create_taxonomy_for_import(), and create_competency_taxonomy(). Documenting it once at the function that owns the behavior avoids it going stale at whichever call site happens to keep the comment.

5. Please explicitly state that there will be a openedx-platform follow-up in the PR description itself.

[alezconsultant]

1. Done, wrap create_competency_taxonomy to try/except and raise DRF ValidationError
2. Add tests for CompetencyTaxonomyView in tests/openedx_learning/applets/cbe/test_views.py
3. Add tests test_create_import_tags_creates_no_competency_row and test_perform_create_tags_creates_no_competency_row in tests/openedx_learning/applets/cbe/test_views.py
4. Add docstring to create_taxonomy to explain logic for ommited export_id passed to create_taxonomy
5. Add statement about future openedx-platform PR

[mgwozdz-unicon]

Approved, but I left some suggestions that I think clean up the comments better. Could you please also update the PR description to say Related to openedx/openedx-core#628 instead of See #628 to see if that connects the Github Issue and PR together?

[mgwozdz-unicon]

Suggested change

	tests/openedx_tagging/test_views.py can't check this directly: it would have
	to import CompetencyTaxonomy, breaking the layering rule it's demonstrating.

This feels like an odd AI relic to me.

[mgwozdz-unicon]

Suggested change

	Doesn't check whether a CompetencyTaxonomy row also gets created for
	"competency". See tests/openedx_learning/applets/cbe/test_views.py for
	that assertion.

This feels like an odd AI relic to me.

[mgwozdz-unicon]

Suggested change

	Doesn't check whether a CompetencyTaxonomy row also gets created for
	"competency".
	See tests/openedx_learning/applets/cbe/test_views.py for that assertion.

This feels like an odd AI relic to me.

[alezconsultant]

Thanks. I updated the PR description and applied your changes to the test comments.